A multiplexing transmission system is a system which assigns input signals supplied from a plurality of transmission channels to different times, different wave lengths (frequencies) or the like, respectively, to transmit them via a single transmission channel. As a multiplexing transmission method of a variable length frame (for example, Ethernet (registered trademark) frame (hereinafter referred to as a MAC (Media Access Control) frame)), a frame multiplexing transmission method is known, which multiplexes each frame of a plurality of variable length frames to transmit them.
The frame multiplexing transmission method will be described with reference to FIG. 1. FIG. 1 is a schematic view showing a frame multiplexing transmission system which executes a frame multiplexing transmission method. The frame multiplexing transmission system includes a multiplexing apparatus 131 and a demultiplexing apparatus 132. The multiplexing apparatus 131 and the demultiplexing apparatus 132 are connected to each other via a transmission channel 134. Each of the multiplexing apparatus 131 and the demultiplexing apparatus 132 has channels (each of which is hereinafter also referred to as a ch) 1 to N (N is an arbitrary integer equal to or more than 1). The multiplexing apparatus 131 supplies variable length frames (hereinafter referred to as information signals) 130-1 130-N as input signals to the ch1 to chN. The multiplexing apparatus 131 multiplexes the information signals 130-1 to 130-N to create a multiplexing signal 135. The multiplexing apparatus 131 transmits the multiplexing signal 135 to the transmission channel 134. In FIG. 1, the transmission channel 134 indicates an occupation state of a transmission band in each ch in the multiplexing signal 135. The demultiplexing apparatus 132 receives the multiplexing signal 135 from the transmission channel 134. The demultiplexing apparatus 132 demultiplexes the multiplexing signal 135 to output information signals 136-1 to 136-N as output signals from the ch1 to chN, respectively.
Here, for example, let us suppose that a non-signal state 133-1 arises in the input signal of the ch2. In this case, an empty band 135-1 arises in the multiplexing signal 135-1. The multiplexing apparatus 131 effectively uses the transmission band of the transmission channel 134 by applying the empty band 135-1 to transmission of information signal of another channel. In the example of FIG. 1, the multiplexing apparatus 131 transmits the information signal of the ch1 by using the empty band 135-1.
The frame multiplexing transmission method multiplexes variable length information signal directly. FIGS. 2A to 2C are views describing a frame multiplexing in the frame multiplexing transmission method. In FIGS. 2A to 2C, A1 to A2, B1 and C1 to C4 indicate frame data, respectively. FIG. 2A indicates frame data on which frame multiplexing has not carried out yet. FIG. 2B indicates frame data on which frame multiplexing has carried out. FIG. 2C indicates frame data on which frame demultiplexing has carried out. Here, in FIGS. 2A to 2C, the A1 to A2 correspond to the information signal 130-1, the B1 corresponds to the information signal 130-2 and the C1 to C4 correspond to the information signal 130-N. In the frame multiplexing transmission method, when an information signal supplied from one specific channel is long, until the information signal is completely transmitted, an information signal supplied from another channel cannot be transmitted. Therefore, the problem arises in which the transmission state of the information signal in the specific channel causes a negative effect on the transmission state of the information signal in the other channel. In FIGS. 2A to 2C, since the frame length of the frame A1 supplied from the ch1 is long, the frame B1 and the frames C1 to C4 supplied from the ch2 and the chN, respectively, are delayed as shown in FIG. 2C.
Such a problem appears particularly in the case that an information signal including data with a high real time property and an information signal including data with a low real time property are multiplexed and transmitted as the effect on the information signal including the data with the high real time property. For example, let us suppose that information signals are transmitted, the information signals including data, which have low real time properties and have large data sizes, such as image data of the CAD (computer aided design) and/or data of file transmission. In addition, let us suppose that other information signals are supplied at that time, the other information signals including data, which have high real time properties, such as voice data of VoIP (Voice over IP (Internet Protocol)) and/or video data of video delivery. In this case, until the data of the CAD and/or the file transmission is completely transmitted, the data of the VoIP and/or the video delivery cannot be transmitted. Therefore, the real time property of the VoIP and/or the video delivery cannot be secured.
In order to solve the above-mentioned problem, a technique is disclosed, which divides a variable length frame of an information signal supplied to each channel into fixed length data, each of which has a small size, and assigns it to a payload of a multiplexing frame in a multiplexing signal.
The patent literature 1 discloses a broadcast transmitting device which can perform effective transmission. The broadcast transmitting device in the patent literature 1 includes a setting means, a creating means and a transmitting means. The setting means sets an assignment of information communication channels to slots provided to a frame. The creating means creates, based on the setting contents by the setting means, a frame in which broadcast-related information regarding the information communication channel assigned to each slot are contained in each slot and information identifying the information communication channel is added to the broadcast-related information regarding the information communication channel. The transmitting means transmits the frame created by the creating means. The broadcast transmitting device in the patent literature 1 can arbitrarily set an assignment of information communication channels to slots provided to a frame which transmits signals concerning broadcasting. Thus, the broadcast transmitting device in the patent literature 1 can perform effective transmission according to the various usage statuses of the information communication channels.
Hereinafter, the broadcast transmitting device in the patent literature 1 will be described with reference to drawings. FIG. 3 is a view showing a configuration of a transmission system according the broadcast transmitting device in the patent literature 1. The transmission system includes a transmitting device 141 and a receiving device 142. The transmitting device 141 and the receiving device 142 are connected to each other by using a transmission channel 144. Here, in the patent literature 1, the transmitting device 141 and the receiving device 142 perform wireless transmission.
First, a configuration of the transmitting device 141 will be described. The transmitting device 141 includes a multiplexing processing section 1411, a modulating section 1412, a transmitting section 1413, an operating section 1414, a controlling section 1415 and encoding sections 1416-1 to 1416-N. The transmitting device 141 receives information signals 140-1 to 140-N of N number of channels as input signals. The encoding sections 1416-1 to 1416-N encode the information signals 140-1 to 140-N, respectively, and output them to the multiplexing processing section 1411. The multiplexing processing section 1411 multiplexes the encoded information signals 140-1 to 140-N to create a data stream (a multiplexing signal) and outputs it to the modulating section 1412. The modulating section 1412 modulates the data stream and outputs it to the transmitting section 1413. The transmitting section 1413 performs a transmitting processing on the modulated data stream and outputs it to the transmission channel 144. The operating section 1414 is an I/O interface between the device and the user. The controlling section 1415 controls the multiplexing processing section 1411 based on inputs from the operating section 1414.
Next, a configuration of a data stream transmitted and received between the transmitting device 141 and the receiving device 142 will be described. FIG. 4 is a view showing a configuration of a data stream transmitted by the broadcast transmitting device in the patent literature 1. The data stream includes successive frames each having the same configuration as others. Each frame includes a frame synchronous signal (hereinafter referred to as UW: unique word) 15021 and information data 15022. The information data 15022 of each frame includes fixed slots of the time-division. In this case, the number of channels: N is 3, and the number of slots of the information data 15022: p (p is an integer equal to or more than 1) is 3. Each slot of the information data includes channel information 15031 and a fixed length data 15032. The channel information 15031 is an identifier of the channel to which the base information signal of the fixed length data 15032 is supplied in the transmitting device 141. The fixed length data 15032 is data that the information signal supplied to the channel indicated by the channel information 15031 is divided into with fixed slot length. The data stream transmitted by the broadcast transmitting device in the patent literature 1 has the above-mentioned configuration.
Next, the creating the above-mentioned fixed length data 15032 to be stored in each slot of the frame in the data stream will be described. FIGS. 5A and 5B are views showing the division of the information signals 140-1 to 140-N into the fixed length data 15032 in the broadcast transmitting device in the patent literature 1. For example, let us suppose that the transmitting device 141 includes 3 channels and 3 encoding sections 1416-1 to 1416-3 corresponding to the respective channels. FIG. 5A indicates the information signals 140-1 to 140-3 supplied to respective channels by the transmitting device 141. The transmitting device 141 supplies the information signal 140-1 to the channel 1, the information signal 140-2 to the channel 2 and the information signal 140-3 to the channel 3. Since the information signals 140-1 to 140-3 are variable length frames, they have the different frame lengths.
Next, as shown in FIG. 5B, the information signals 140-1 to 140-3 are divided into fixed length data 161-1 to 161-r, 162-1 to 162-r and 163-1 to 163-r (r is an integer, r>0), respectively. The encoding sections 1416-1 to 1416-3 divide the information signals 140-1 to 140-3 into data with the same sizes as the fixed length data 15032, respectively, to create the fixed length data 161-1 to 161-r, 162-1 to 162-r and 163-1 to 163-r. These fixed length data 161-1 to 161-r, 162-1 to 162-r and 163-1 to 163-r are the fixed length data 15032. As described above, the fixed length data 15032 are created from the information signals 140-1 to 140-3.
Next, the multiplexing processing in the multiplexing processing section 1411 will be described. The multiplexing processing section 1411 multiplexes the fixed length data 15032 supplied from the encoding sections 1416-1 to 1416-3 by assigning the fixed length data 15032 to respective slots in the frames in the data stream. The multiplexing processing section 1411 assigns the fixed length data 15032 to the respective slots based on the assignment condition specified from the controlling section 1415. For example, let us suppose that the multiplexing processing section 1411 receives the assignment condition from the controlling section 1415.
<Assignment condition 1>: All channels have information signals.
Slot 1=ch1, Slot 2=ch2, Slot 3=ch 3
<Assignment condition 2>: The ch 2 does not have information signal and the other channels have information signals.
Slot 1=ch1, Slot 2=ch1, Slot 3=ch 3
FIG. 6 is a view showing the assignment status of the fixed length data to the respective slots by the multiplexing processing section 1411 in the broadcast transmitting device in the patent literature 1. The multiplexing processing section 1411 adds UWs 15021 to the information data 15022-1 to 15022-6, respectively, and output them to the modulating section 1412, in this order. The channel information 15031 and the fixed length data 15032 are stored in each slot of each of the information data 15022-1 to 15022-6. The multiplexing processing section 1411, during the information data 15022-1 to 15022-3 in which all channels have information signals, the slot 1 is assigned to the ch1, the slot 2 is assigned to the ch 2 and the slot 3 is assigned to ch3 based on the above-mentioned assignment condition 1. On the other hand, the multiplexing processing section 1411, during the information data 15022-4 or later in which the ch 2 does not have information signal and the other channels have information signals, the slot 1 is assigned to the ch1, the slot 2 is assigned to the ch 1 and the slot 3 is assigned to ch3 based on the above-mentioned assignment condition 2. The multiplexing processing section 1411 transmits the data stream multiplexed as mentioned above through the modulating section 1412 and the transmitting section 1413 to the transmission channel 144.
Next, with reference to FIG. 3, a configuration of the receiving device 142 will be described. The receiving device 142 includes a receiving section 1421, a demodulating section 1422, a demultiplexing section 1423 and decoding sections 1424-1 to 1424-N. The receiving section 1421 receives the data stream from the transmission channel 144. The receiving section 1421 performs a receiving processing on the data stream and outputs it to the demodulating section 1422. The demodulating section 1422 demodulates the data stream supplied from the receiving section 1421 and outputs it to the demultiplexing section 1423. The demultiplexing section 1423 identifies each frame by using frame synchronization based on the UW15021. The demultiplexing section 1423 demultiplexes the fixed length data 15032 from the slot of each frame. The demultiplexing section 1423 outputs the fixed length data 15032 to the corresponding decoding sections 1424-1 to 1421-N based on the channel information 15031. The decoding sections 1424-1 to 1424-N decode the fixed length data 15032 to reproduce the information signals 146-1 to 146-N. The decoding sections 1424-1 to 1424-N output the information signals 146-1 to 146-N to the channels 1 to N, respectively.
As shown above, in the broadcast transmitting device in the patent literature 1, the multiplexing processing section 1411, even if a certain channel does not have an information signal, assigns an information signal of another channel based on an assignment condition previously supplied from the controlling section 1415. Therefore, the broadcast transmitting device in the patent literature 1 can perform effective transmission by effectively using an empty band of a multiplexing signal.
As a related technique, the patent literature 2 discloses a preferential transmission system which can preferentially transmit (high priority) data with high importance during low-priority-data transmission.
In addition, the patent literature 3 discloses a method of controlling data transfer of a switching device which can perform data transfer with an arbitrary rate in an arbitrary channel in a data transfer with the time-division multiplexing mode.
Furthermore, the patent literature 4 discloses an ATM communication method which can improve a transmission efficiency of a downlink in a down link communication from a base station to a terminal station.
The first problem of the patent literature 1 is that if the number of slots: p in the information data 15022 is not equal to the number of channels: N in the transmitting device 141, the band assignment with an arbitrary ratio with respect to the channels cannot be carried out.
This is because the assignment condition set to the multiplexing processing section 1411 from the controlling section 1415 is static with respect to the slot. For example, let us suppose that the number of slots: p is 4 and the number of channels: N is 3. FIG. 7 is a view showing the assignment status of the fixed length data to the respective slots by the multiplexing processing section 1411 in the broadcast transmitting device in the patent literature 1. Each slot of the information data 15022-10 to 15022-12 includes the channel information 15031 and the fixed length data 15032. Here, let us suppose that the assignment condition, for which all channels have the fixed length data 15032, is the slot 1=the ch1, the slot 2=the ch1, the slot 3=the ch2 and the slot 4=the ch3. As shown in FIG. 7, the multiplexing processing section 1411 can perform the assignment of the fixed length data 15032 to the information data 15022-10 to 15022-12 based on the assignment condition. In this case, a channel multiplexing ratio of ch1:ch2:ch3 is 2:1:1. However, when the channel multiplexing ratio of ch1:ch2:ch3=1:1:1 is desired, it can be realized only by not using any one of the slots 1 to 4. In addition, when the channel multiplexing ratio of ch1:ch2:ch3=3:2:1 is desired, it cannot be realized because the number of slots is less than 6 which is the necessary number of slots.
The second problem is that if a certain channel does not have an information signal and another channel has an information signal, the information signal cannot be assigned to an empty band with an arbitrary ratio with respect to the channels.
This is because the assignment condition, for which a certain channel does not have an information signal, set to the multiplexing processing section 1411 is static with respect to the slot. For example, let us suppose that the number of slots: p is 3 and the number of channels: N is 3 and the multiplexing processing section 1411 sets the above-mentioned assignment conditions 1 and 2, as described with reference to FIG. 6. The information data 15022-1 to 15022-3 depend on the assignment condition 1 and the multiplexing ratio of ch1:ch2:ch3 is 1:1:1. On the other hand, the information data 15022-4 to 15022-7 depend on the assignment condition 2 and the multiplexing ratio of ch1:ch2:ch3 is 2:0:1. In this case, when the ratio of ch1:ch3 is tried to be 1:1, it can be realized only by not using the slot used by the ch2. Therefore, the transmission efficiency is decreased.
The third problem is that a band loss arises because a transmission band for adding the channel information 15031 to each fixed length data 15032 is required.
This is because the channel including the fixed length data 15032 stored in each slot of the information data 15022 is different based on whether or not the fixed length data 15032 exists in each channel of the transmitting device 141. Therefore, in order to demultiplexing the data stream appropriately on the side of the receiving device 142, the channel information 15031 has to be added to the fixed length data 15032. As a result, in the transmission of the data stream, the band for the channel information 15031 is inevitably consumed.